1. Field of the Invention
The invention relates to laser systems and more specifically to actively tuning components in a laser system.
2. Related Art
Nearly all high peak power USP laser systems use the technique of chirped pulse amplification (CPA) to produce short-duration high-intensity pulses. Chirped pulse amplification increases the energy of a short pulse while avoiding optical amplifier damage. In this technique, the duration of the pulse is increased by dispersing it temporally as a function of wavelength (a process called “chirping”), amplifying the chirped pulse, and then recompressing the chirped pulse to significantly shorten its duration. By lengthening the pulse in time, energy can be efficiently extracted from an optical amplifier gain medium while the peak power levels of the pulse are below the damage threshold of the optical amplifier.
The dispersion in CPA laser systems can vary due to many factors. For instance, most CPA systems rely on Treacy compressors to reform pulses after they have been amplified. The optical path in a Treacy compressor is relatively long and is mostly through air. The refractive index of air may seem negligible, but it can vary the operating wavelength of the system from that of a vacuum by ˜0.5 nm at ˜1550 nm. The refractive index of air varies with temperature, pressure, and relative humidity, so changes in environment can affect system performance. The dispersion of various other components in a CPA system may also vary with environmental conditions, such as Bragg fiber and fiber Bragg gratings (FBGs). The refractive index of system components can vary with pulse intensity via optical nonlinear processes, which can also induce optical phase variations similar to dispersion and ultimately effect pulse duration.
The manufacturing tolerances of some components, such as Bragg fiber and FBGs, can result in a wide variation in the dispersive properties of different fibers. It is also impractical to fine tune the dispersion of each laser system in a mass manufacturing environment, since the output of each system must be measured and then its dispersion must be fine tuned.